Preparation of a surficially calcined natural carbonate catalyst



NOCI ZH MEHF @ZHPQNRO B. B. CORSON ET AL Original Filed Dec.

PREPARATION OF A SURFICIALLY CALCINED NATURAL CARBONATE CATALYST Oct. 21, 1952 3 ss vd aad aNaaAls o L aalaamoo aNazNaa-MHJ.; Nan aad Hala/A Patented Oct. 21., 17952 mtraRAfrIoNfoF A SURFICIALLY onL- TCINED NATURAL. CARBONATE- CATA- i LYST Ben'Bennett Gerson and George Arthur'Webb, Pittsburgh;-Pa..; assignors tofKoppersCompany,

Inc.,Y arcor-porationI of Delaware .,Qxrigqinal application-December 31, 1943, SeriaLNo.

516,352'. 'Diridedand thi'sapplioation September ,25,194,7521'1'131 N0- 7716,130

"1 "The present invention'relate's-inngeneral tordehydrogenation catalysts and; their f composition and comprehendsl 'improvements inx the -catalyst and 1theircomposition*to` adapt them more r.especially"v to the dehydrogenation of .aliphatics vand particularly tothe dehydrogenation ofthe Vjaliphatic side-chains Vof alkylaromaticswhaving a plurality ofcarbon'atoms in said iside chains; for example, ftheconversion of isobutane to' isobue tylene and of. ethylbenzenes into styrenes.

"More, particularly 'the present'v invention is di` rected to' 'the method of preparing the catalyst described in our copending applicationiseriaPNo. 516,352, led December 3 ,1,"'19 4V3, nowjPatent 2,444,113S,of.lur1eg29,V 194,8, of Whioh'ithis applicationv is a division.

' An object of the present 1 invention; isjthe Aplovision of improved ,and less expensive'jorms of theknown catalystsof lime, magnesia, and mixturesithereof' for example with, orwtholltyiron oxide'Y forv ,carryingV ,on reactionsv hel omgingA tofthe above-stated clas ses,. wherein thel catalyst` compositev comprises a Vmajor,portionjoy Weightof the .carbonatesof their metals, ,oalcumand magnesium, and theac'tive catalyticl medium comprises` the oxide ofithe metals, as., a minorAv portion by Weight of 'the Acatalyst. composita., wherebythe greater structural 'strength ofthe carbonate form of,l the ,metalspredominateszinthe. composite; thus making 4`unnecessary pelleting Vofithe oxide, or vsupporting' ,the `Oxide of the, metalspnextraneous carriers, to` proyide equivalentgsturdness to'the composi te,.in order to elimnaterushioe andV packing ofthe .oxiiclein .catalyticnsa hereinafter described. y

. Ailfurtherjobj ect, of improvementgis.tomrovide forlthe presentuses easily= available natural. minerais and other naturally-occurrioaproducts that are `easily convertible either by.,13.111213?.efilllentL or automatically in use, to catalystcomposites;for for the stated. purposes.

A further object ofl invention is ,toV provide improvements bothiforthe preparationaald .Subsequent operation of catalyst composite ofjthe stated .types rwhereby,their physical `:lot'curity.2.11101 effective'activity fcan be assured. over, importantly prolonged operating. periods.

An important-feature ofthe-present invention is the' provisiongoff a4 catalystgcomposite composedof granules of calcium and-magnesiumcaloined at a temperature between ,600 and650C., 'since applicants"I haverfound; as --is v hereinafter pointed-out; that"under-'identical catalyzing-conditions `v`the catalytic 'conversion withA dolomite VcalcinedatilliCi'elncreased from f22% -to 33% 2 overv that Which-`obtains with the same 1 dolomite calcined at 920 C.

A furtherimportant feature of the-presentinvention `is vthe discovery, as hereinafter also pointed out, 'that-bythe use of-natural carbonates which upon cal'cination to constant weightw'ould show af loss of- 3045%,a farUsuperior--catalyst results, from-l the standpoint of providing-better yields and catalytic conversions', than-isV possible with like carbonate rocks which shows-a-loss of. as little as l 21 by Weight upon complete ignition.

The invention has Vfor-further objectszsuch other improvements and such other operative 'advantagesor results' asmay'- be found tol obtainrin the processes or apparatus hereinafterdescriloed or claimed.

It` is. known -that tooth*limearid rnagnesia, either individually or in admilxture, y or containing a fractional proportion ofiron oxides,-providegood catalystsy for dehydrogenation reactionsinvolving especiallythe aliphaticl-side-chainsof alkylaromatics. '-The lime and--magnesia-as usually prepared are either pulverulent -or-,--structurally, highly friable lumps; and htheir successfuluse hasjheretoore necessitated, in orderto provide them with'the 4required resistancevto crushing and packing demanded in large-scale operations; that these Vmaterialsdoe made upasa compositehy being formed intopellets or by'bein'gfsupported .0n structurally sturdy carrierssuch as active carbon, silica gel,-F1orida earth,- or the like-which alsoprovide the large surface areaswhereby said compounds are brought into -intimate contact with the aliphatic or alkylaromatic compounds-to ,be dehydrogenated.

It ,has now been found by the-present. co-inventorsfthat particularly desirableandi-rugged forms ofJ lime Aand `magnesia with or without-appropriate contents, forex-ample, of iron-oxide can be easily prepared bythe c alcination'at-the known range vof suitable temperatures ofsurflcial portions onlyof'granules of Asuch-natural products as marble; limestone; dolomite,HV dolomite limestone, andthe like; aswell as vcertain` other natural modicationsof said-substances containing`-iron oxide, -as willbehereinafter'inamed and particularized. `:.By iperformiiflg;therY known toalcination of the.4 granular i said .'cn'aterialstsov :that the required @evoluti-@noi 'carbon dioxidewis -restricted. substantially ,completely-to fthe 'outer portions of the .granules leaving-as `is hereinafter pointedV out f in Examples f No.:v 1 ,and ,No2, ar bonate f cores comprising` the maior, portion by weight of the. catalyst article, or 'composita :the high resistance. to crushing. ,and-,the i sturdystruc- 3 ture naturally inherent to the carbonate of the limestone, dolomite, et cetera, can be in greater part preserved as a major portion by weight ofthe granule in the interior cores of the granules and their outer portions will comprise, to a depth determined by the extent of calcination, a minor portion by weight of the granules as a coating of the required catalytic oxide, or oxides, a minor portion by weight of the granules as that is adequately held and supported without other means by the natural carbonate material of the cores themselves, thus providing, relatively simple and cheaply, granule composites of the required lime or magnesia as the vitalizing catalytic material, having as its component for sufficient structural strength a greater mass or weight of the stronger carbonate, rather than the weaker oxide, that they can be used in beds of considerable depth and for relatively prolonged periods without substantial deterioration. Advantageously also, if the outer minor portion by weight of oxide-coatings of the so-prepared composite granules are gradually removed from their inner supporting cores of carbonate constituting the major portion by weight of the composite article, during prolonged operation as may result, for example, from erosion of the vapors of the reaction mixture flowing thereover, it is possible, according to expedients and procedures that will be hereinn after described, even without removing the composite granules from the dehydrogenation reactor, to form new minor quantities of coatings of the oxides on the said granular cores by further calcination-conversion of the material of the cores themselves to said oxides, and such further calcination-conversion can be practically carried on at spaced intervals until theoretically the whole material of the cores is completely converted to oxides for catalytic use.

According to the invention, therefore, organic compounds of the classes represented by isobutane and ethylbenzene are dehydrogenated to give sobutene and styrene, and the like, by flowing said compounds in vapor form admixed with water vapor, and in certain instances with a minor amount of added carbon dioxide, at either subatmospheric, atmospheric, or super-atmospheric pressures, through a reaction zone containing catalytic granules comprising, each a structurally resistant core of the carbonate of calcium, or of magnesium, or mixtures of said carbonates containing or not containing iron oxide, in which, as is hereinafter more particularly pointed out in Examples No. 1 and No. 2, the carbonate cores constituted the greater mass or weight of the catalyst composite granules, and an outer layer of an oxide or mixture of oxides oi said metals, that is preferably structurally integral With said core, such a product resulting, for example, from the heating of a granule of such naturally occurring rocks as limestone, dolomite, dolomitic limestone, and ferruginous limestone. These stony materials may also contain, for example, minor proportions of alumina and silica, or other oxides, without important loss of utility for the present purpose; it is, however, undesirable to have any important proportion of their calcium, magnesium, or iron contents vin such combination with said alumina, silica, or any other compound, that their oxides are not freely liberated and remain in that form during the calcination and subsequent cooling of said stony materials. A simple criterion of the appropriateness of a said natural rock for the present purpose is its percentage loss of weight upon complete ignition which is indicative of the amount of the oxides of calcium, magnesium, or iron that can be liberated from their carbonates by the calcination step. Good results have been obtained with carbonate rocks that showed a loss of as little as about 21% by Weight upon complete ignition, even though their ultimate analyses showed them to contain as much as about 36% by weight of silica. Better yields and conversions to said dehydrogenated organic prod-- ucts have, however, been obtained, in the practice, by catalytically employing granules, as above-described, that resulted from the surcial calcination of those said stony materials which, upon calcination to constant weight (total possible loss upon ignition), showed a loss of from about 30% to 45% by weight.

In the preparation of the catalytic granules of invention, by calcination of natural rocks containing carbonates of lime, magnesia, and the like, the temperature of calcination is of considerable import as to the activity of the oxide in catalysis, the calcination being preferably carried out within the temperature range of about 60G-650 C. instead of the 900 C., or above, temperatures usually employed in the art when said rocks are calcined for their complete conversion to lime, magnesia, or mixtures thereof. As is hereinafter further more particularly pointed out, the catalytic efciency of the oxide is increased from about 22% to 33% by restricting the calcination to 600-650 C., as compared with calcination at 900 C., and catalytic use, under equivalent conditions.

The thickness of the layer of said metallic oxide, or oxides, supported on the carbonate core of the catalyst granules depends, amongst other factors, upon the temperature of calcination and upon the length of time the raw rock granules are treated at said temperature. For the present dehydrogenation reaction, a good catalytic surface condition has been produced in granules of a specific dolomite by calcining the granules at 650 C. for three hours. In the case of a dolomite from another source the best producible catalytic surface condition had not been produced even after twelve hours of calcination at 650 C The duration of the calcination step to achieve the optimum catalytic surface condition for the purpose should be determined empirically for the speciiic raw rock to be employed. It can in general be said, however, that when the calcination step is performed outside the dehydrogenation reactor apparatus and consequently in the absence of any materials undergoing dehydrogenation, as for example in any heated zone capable of maintaining the rock granules in the stated 600 to 650 C. range of temperatures and of permitting'free exit of the evolved gases therefrom, a satisfactory catalyst product can be ordinarily produced in between three to twelve hours in the case of raw carbonate-rock granules that pass through and are retained cn, respectively, screens of four and ten mesh. ln the cases of dolomites, limestones, and the like, containing also iron oxide, or carbonate of iron, the calcination period can be reduced below that which would otherwise obtain, because the presence of iron assists in the decomposition of calcium and of magnesium carbonates into their oxides and carbon dioxide.

As above indicated, the raw carbonate-rock granules can be converted to the catalyst of invention in the above-prescribed manner before they are installed in the dehydrogenation reacderrate* 5 toriand before: theforganicfcompounds'to'be "dehydrogenated are brought into contact therewith. lIn other words,A the rawvcarbonate-rock granules canbe activated by a precalcination step.

The preparation ofthe instant novel catalyst products is, howeven'not limited to such precal'cinatio-n step,"because:substantially the same said `productsiand reactivities thereof can be achieved by surficial calcination of the raw carbonate-rock `gra1f1ules"in situA in 'the dehydrogenationreactor by merely iiowing thereover steam, or vapors of.` the'organic compounds to vbe dehydrogenated'or lmixtures thereof, 'that have been preheated'to-within the 600-700 C; temperatures range required for dehydrogenation'of said organic compounds.

Since the carbonate compounds'ofl the' metals calcium,magnesium, kand iron show little catalytic activity to promoter dehydrogenations 'of the organic compoundsbut'theoxides of said metals,` 4left asf calcination-residuum `of said carbonates, are highly effective for the purpose, in those instances, Where the raw carbonate-rock granulesv are catalytically activated ,in'situ in the dehydrogenation reactor, it will be found that the full activity of the so-formed catalyst product is not achieved vimmediately but :is progressivelyattained after a relatively extended induction period. lfthe .activation of the rawcarbonate rock is `accomplished by Vlowingthereoverat about 650 C. La' mixture of `some steam and `vaporsrof the organic compound' tovbev dehydrogenated it' will beobserved, during'the initial period ofv passing of such' vaporous' mixture, that little Orino dehydrogenation of lthe .employed 'organic compound will beeffected. With-continued passage, however,` of said. vaporous mixture,` the dehydrogenationofa relatively minor proportion tof vthe so-passed organic compound willbe detecte-din reaction-products issuing from contact with' the carbonate-rock;` this inidcatesithat asmall amount of the-metallic oxide, or oxides, has been formed on the.` surface thereof. With further: continued passage of said vaporous mixture, .the l, formation ofmoref andzmore of "the oxides isA indicated by increasingcontent of dehydrogenation'product of theorganic compound in said. reaction-products. With :continued increase of oxide-formationon thesurface ofthe l carbonate-rock, there will ultimately `be reached azstage'rwhere, if the proportion of employed steam. :is inadequate, the produced oxide-surface becomesy so Aactive that they deposition` thereon of carbon,:resulting from unwanted incidental sidereactions that are upyrolytically destructive of the employed organic compound and do not` represent its Wanted'mere dehydrogenation product, willpsoon tend to Yobscure `and y eventually will quench the catalytic activity of the formed oxide-surfaces on the carbonate-rock granules. Such quenching of the catalytic activity .Will eventually. necessitate cessation of operation` and either treatment; of the catalyst'granules for removal ofthe deposited `carbon or their replacement byznew material.

The :present inventors have z now found,l however, that if the `proportion ofsteam in themixture L1 thereof with' the to-be-dehydrogenated organic compound." introduced into the dehydrogenation'reactor, is continuously maintained at a leveltadequate to react with f the said'deposited carbon according'to thewater-'gas'reaction (lime andrimagnesiafare 'alsoiknown catalysts for` the watergf'gaszreaction) theacatalytic"oxideecoatings 6^ of *the carbonate=rock granules 'can bermain-i tained `:effectively free: of fsaid vcarbon :and their activity l'will f continue ffori protracted periods Ito remain Aunimpaired `'for Ldehy'drogenation purposes.

The leiectivenlife off the present acatalytic'fmaterial does not,-however, 'depend merely: onl providing oxideecoatings for the\carbonaterock granules, .or 4on lmaintaining saifd-` coatings.v during operation substantially? free o'f"depos`ited carbon, for the reason ithat hthe l carbonate mores, upon which; the'rcatalytic-material depends Ffor its con-4 tinued structural integrity, exhibit 1 in ther'rcactionl zonegwithinfthe effective ltemperature-range of` dehydrogenation,r` a: positive:partial `pressure `of carbon 'dioxide which can! lead? to 'the Hmorezor less rapid: disintegration; of the="carbonatef-coretand consequent-loss ofr'utility" ofthe catalystmaterial.

The i present limprovement, -therefore A"further providespwhen:employ-ing 'the catalysts of? invention, for observancef'and' regulationfof the carbon-'dioxidepartial pressure? inl the zone of dehydrogenation duri-ng ydivers periods: vof-a cycle loi. operation. "In those instances,=where the-oxide coatings are `formed .on the rock-carbonate granules "in situ inthe dehydrogenation reactor, as above described, therate `oflflovvof-'vapor thereover must be sufficiently Vrapid,"during-the induction or oxide-forminglstage, to maintain the partial pressure of carbon dioxide in the reactor atmosphere below at most the decomposi-l tionpressure of the rcarbon dioxide evolved'y from the employed rock-carbonate granules at the existing reactor temperature; otherwise, V.there will be no oxide formation and the catalyst product will not develop. During this said induction stage there should alsoY be at all times sufficient proportion of steam in the said flowing mixture of reactants both to forma Water-gas with any carbon incidentally deposited on the metallic oxide coatings undergoing formation andalsoV to remove, from the reactor, any so-formed carbon dioxide at a partial pressure less than the carbondioxide decomposition pressure of the rock-caru bonate; otherwise, any previously formed metallic oxide will be reconvert-ed into thecatalytically inactive metallic carbonate. Ultimately, in the cycle of operation, when sufficient of the metallic oxide, or oxides, has been formed` on the surface of saidgranules to producean effective catalyticcoating thereof, the partial pressure of 1 carbon dioxide in the reactor atmosphere, in the interest of preserving the rock-carbonate cores of the catalyst, granules and consequently their rugged structure, must'be increased, for example by decreasing the steam component of the. catalytically treated mixture of steam and organic compound, to a point where said partial pressure is at least about equal to the carbon-dioxide decomposition pressure of saidrock-carbonate at the reactor temperature. If` the carbon-,dioxide partial pressure in thereactor is allowed much to exceed the decomposition pressure ofthecarbonate in respect of carbon dioxide, the metallicoxide coatings Wil1of course, revert to the catalytically inactive. metallic carbonate .atzarate corresponding to the degree of `excess at which saidv partial pressure is allowed to obtain.v

From the above-recited, itobviouslylies within the skill of the operator, byappropriate control of the carbon-dioxide, partial pressure in the atmosphere in the dehydrogenation reactor, to form therein from the raw carbonate-rock granules the active i dehydrogenation catalyst-product of 'the invention, to retain it in its active form, to preserve its physical structurey through protracted cycles of operation, to maintain it effectively free of carbon deposited thereon by incidentals, unwanted side-reactions, and also to reduce, if necessary, any excessive reactivity thereof.

Manifestly, in those instances Where the rockcarbonate granules are precalcined outside the dehydrogenation reactor to their Wanted activity, it only remains `for the operator to provide, in the admixture'of steam and organic compound introduced into the reactor, that quantity of the former component which prevents eiTective deposition of pyrolytic carbon on the catalyst surfaces and also gives a partial pressure of carbon dioxide in the reactor atmosphere that is at least substantially equal tothe decomposition pressure of the rock-carbonate in respect of said gas.

The partial pressure of carbon dioxide that should be maintained in the reactor atmosphere at various stages in the above-described operating cycle will vary from application to application and also with the nature of the raw carbonate-rock employed, as is indicated by the following table showing the carbon-dioxide partial pressure, at the dehydrogenation temperature of 650 C., of some natural products that are useful for the present application:

Magnesia, as Well as that natural mixture of lime, magncsia, and iron oxide formed by the calcination oi' certain ferruginous dolomites, provide especially reactive dehydrogenation catalysts. However, the raW-rock-carbonates from which they are formed, as shown above, have relatively high partial pressures of carbon dioxide at 650 C. and in the practice it has been found that catalyst-supporting cores of such materials when einploying the most practical ratio of steam to organic-compound vapors introduced in the dehydrogenation reactor, are not as easily retained in a structurally stable condition as obtains in the case of the dolomite and limestone cores. This is principally in consequence of the fact that the carbon incidentally deposited, as aforesaid, on the catalyst-surface during operation is insumcient when removed therefrom by means of the watergas reaction to provide adequate partial pressure of carbon dioxide in the reactor atmosphere completely to prevent substantial decomposition of the magnesite and certain ferruginous dolomite cores during protracted operating periods. In their cases, it has been found advantageous to add to reactants passing to the reactor, carbon dioxide from an outside source, for example combustion-products, in quantity suiiicient to provide lin addition to that carbon dioxide which is formed by the said low-temperature Water-gas reaction, a carbon-dioxide partial pressure in the reactor atmosphere that is at least about the decomposition pressure of carbon dioxide of said carbonate materials.

' In the accompanying Fig. 1 of the single drawing forming a part of this specification, there is graphically shown the operative effects that can be obtained by careful observance and control of the carbon-dioxide partial pressure of the reactor-atmosphere when employing an improved catalyst of invention. The single curve of said ligure represents the operating effects and results obtained in the employment of a said catalyst that was prepared from dolomite granules of sizes of 4 to l0 mesh. These granules were partially activated by their heating for three hours at about 650 C. after which they were charged into the dehydrogenation reactor, With their so-produced suriicial coatings of a mixture of lime and magnesia. Their complete activation was effected in situ in said reactor by flowing thereover at a temperature of about 650 C. a preheated stream of mixed steam and vaporous ethylbenzene in the respective ratio by volume of approximately 10:1 while employing a contact time of 0.9 second. Hours of operation are plotted in said gure as Iabscissae and the percentage conversion, by Weight, of ethylbenzene per pass over the heated catalyst is plotted as ordinates.

From an initial conversion to styrene of about 26% by Weight of the ethylbenzene brought into contact with the dolomite granules that had been merely precalcined for three hours, the conversion of ethylbenzene to said product increased, after about eighteen hours of the described operation, to about 37%, per pass over the catalyst, and continued at this conversion level for the next about forty-seven operating hours. After about the rst tWenty-ve or thirty hours of the described operation, as shown by the curve of Fig. 1, the catalyst had reached substantially its full activity and continued so to function, Without diminution, to the sixty-fifth hour. These results show that with the specific dolomite employed, a mere three-hour precalcination period was insucient to provide the dolomite granules With their most active thickness of oxide-coating which Was later achieved in actual o eration. During the said forty-seven-hour operating period, there was substantially no deposition of carbon accumulated on the catalyst surface and the partial pressure of 4carbon dioxide in the reactor atmosphere was in substantial equilibrium with the decomposition pressure of the dolomite cores of the catalyst in respect of carbon dioxide, and the catalyst retained its rugged structure unchanged throughout said operating period. If the above steam-to-ethylbenzene ratio had been sufficiently greater than that employed to have diluted the water-gas-derived carbon dioxide to a point Where its partial pressure was less than the decomposition pressure of the catalyst cores in respect thereof, the catalyst would have lost its sturdy physical structure and, in a time interval corresponding substantially proportionally to the degree of such partial-pressure reduction, would have changed completely, although still active, to a highly friable mixture of lime and magnesia that would rapidly disintegrate and pack and give rise to inoperative resistance to flow of vapors through the reactor. Conversely, if the proportion of steam in the vaporous mixture introduced into'the reactor had been so low that pyrolytically formed carbon was either inadequately removed from the catalyst surface by the lowtemperature Water-gas reaction, or, was even soremoved but at a carbon-dioxide partial pressure in the reactor atmosphere somewhat greater than the decomposition pressure of the catalyst cores in respect thereof, the active lime-magnesia coating of said cores would have been more or less rapidly, respectively, either smothered by carbon or have been converted to the catalytically inactive carbonates of lime and magnesia, and in eitl'ieneyent. theiactivity of the; catalyst would liavasoonbeenlost.

Referring again to the curve of Fig. 1, this urgency of control. ofv the. carbon-dioxide partial pressure-"intthedehydrogenation reactor in the interestporfensuring a long effective life of the catalyst body isforcefully demonstrated. The curvezof said gure shows, ,asabovelrecited that atfthes'sixty-fth .operating hour and under the stated operating conditions about 37% ofi the ethylbenzene' passed over the' catalyst was converted to `styrene and that the process system had'been'in equilibrium for aboutV 35 operating hours; At' the-end of the sixty-fth hour, suficient carbon-dioxide from an extraneous source was-.introduced into the ethylbenzene steamadmixtureeflowing; tothe dehydrogenating reactor to-raisethe carbon-dioxide partial pressure of theeatmosphere therein to .about 35.mm. Hg; i. e.,

to .-abouttwice the decomposition pressure ofthe d dolomite cores of. catalyst granules :inrespect of said carbon dioxide. The eii'cency of conversion of ethylbenzene to. styrene started immediately to decrease and in twelve hours had been reduced to'only about v20% by weight'of the treated ethylbenzene in consequence of the conversion ofthe lime-magnesia coatings of the catalyst granules to their inactive carbonates. Thereafter, the extraneous introduction of carbon dioxide was discontinued and the carbon-dioxide partial pressure in the reactor was decreased, for example, by increasing the proportion of steam in theA ethyl-benZene-steam mixture employed until the carbon-dioxide partial pressure in the reactor. became less than the decomposition pressure of the. dolomite in respect or carbon dioxide, andlafter about forty additional hours of operation, the activity of the catalyst granules hadlbeen completely restored to that obtaining before. introduction of the extraneous carbon dioxide. The proportion of steam insa-ld admixtur'e was then restored to the 10:1 ratio originally obtaining and the styrene production was maintainedfor about twenty hours at the originally highflevel. Thereafter, the described cycle was repeated, as shown in the linal portion of the curve; in conrmation of the above.

The accompanying Fig. 2 shows by means of its two curves the distinction in catalytic activity,

for the present purpose, between dolomitic limey stone granules that had been calcined at a temperature of about 920 C. and the same 'dolomitic granules that were surcially precaleined for l2 hours ata temperature of 650 C... the surfaces thereof beingf further activated-and brought to maximum activity in situ in the dehydrogenationreactor during actual conversion of ethylbenzene .to styrene at 650 C. The curve formed bythe line A represents the conversion capacity of.- the dolomite'that was calcined at the higher said temperature whereas the line B shows the activity of the same raw material prepared at the lower said temperature and only surficially calcined. The operating conditionsduring'both run periods were maintained substantially the same; i. e., the conversion temperature of ethylbenzene to styrene was 650 C., the steam-ethylbenzene ratio was :1, and the contact time was 0.9 second.

Reference to the above curves clearly shows that inthe caseof dolomite calcined' ata temperature'of about 920 C., the'conversion of ethylbenzene vto styrene through seventy hours of said operation .never exceeded more than. .about 22% by, Weight.. of.y ethylbenzene ,per pass` whereas vin the case of. the same:dolomitersurficially 'calcined atf650 C., the said conversion exceeded that of theformer material after aboutfteen hoursof operationfandincreased, at about forty h'oursto about 32-33% and so continued` for the remainder of an operating period of.r 140 hours whenwoperation was discontinued;-

As hereinbefore mentioned,- a. wide variety-of minerals, rocks, and other natural` products containing .carbonates ofcalcium and .magnesium are` of utility fortheV presentpurpose ranging from pure.. magnesites, dolomites.: dolomitio limestones, limestones, marbles;.and..also.these materialsv containing impurities. such asy silica, metallic .oxides and Y.especially an. oxide, or oxides of iron.

When employing substantially the same .Y operating, conditions, the. by-weight. conversion` of ethylbenzene .to styrene. per.. pass over. suriicially calcined magnesite and .dolomitais higher than is` the casewith limestone, i. andthe dolomiteis preferable to. the .magnesite because,. even .though the magnesite is slightly the more Yselectiveor the ethylbenzene conversionpit has such.a relatively high deoomposition pressure in respect of carbon dioxide within fthe: range of temperatures wherein it is catalytically active to promote-.said conversion thatextraneous l carbon dioxide may need .addition to the atmosphere of thedehydiogenation reactor to prevent complete disintegration of. the' magnesite cores. of the catalyst granules if prolonged us'eofthatcatalys't is an important factor, and alsoibecausethe surcial coatingsof magnesia are lessreactive than Ythe lime-magnesieJ coating providedby a dolomite to promotethe low-temperature water=gas reaction whereby pyrolytically-formed carbonA is inhibited accumulating on the catalysts surfaces. Thus the magnesite coatingsare morelikelytobecome coated with carbonthan are coatings ofia mixture' of lime and magnesia.

Ferruginous limestones have been found of special merit for the present purpose. n Upon surcial calcination, they, provide a mixture of the oxides of calcium, magnesium, and iron. They can be prepared accordingto the-invention `as catalytic granules of suchstablestructure and crushing strength that they.l are useful in large-scaleoperations. Representative o1 this latter class of natural products are those found in deposits'rlocated atClinton; NewYork, and are obtainablein the trade aslow-jgrade iron ores. Materials from this source and* known in' commerceV as Red' Fluxes Nos. 1 and 2v are'of: especial utility,l the former containing aboutf30%rFe2O3 and the latter about 12%. of the same, the remainder being essentially.l dolomitic limestone and, a minor amount Vof silica. Under'essentiallyA the same-op.- eratingconditions the surficially. calcined No. 2 Red Flux' granules'gave. an average conversion of ethylbenzene to'styrene of"48%.by weight per pass .of a :1 mixture respectively of steamfand ethylbenzene thereover at a conversion temperatureoff650 C.`wh`ereas the Red Flux Nor 1l gave-an average conversion ofslightly less; matie-421%'.

Those surcially calcined granulesV of' limestones, dolomitic limestones, or dolomitesthat contain essentially no v other. metallic `oxides can be advantageously treated for their increased activity with .minor proportions of, for example, iron oxide, or nickeloxide applied in .any expedient manner land preferably in a fashionthat will obviate slaking ofthe sur'cial coatings of the oxides of calcium, magnesium, or both; for example, suspensions ot.V said.-oxides. ofaironlor: of

nickel in a non-hydrous medium can be sprayed over the said calcined granules. Similarly, it is also feasible for purpose of increasing the resistance to erosion of said suriicial coatings to disperse therein a relatively minor proportion of a salt, or the like, for example a compound of silica, that functions at the temperature of dehydrogenation to form a fibrous skeleton of silicious material therein.

The following examples are illustrative of results that have been obtained in the practice of the invention; in said example, the term average per cent conversion indicates the proportion by Weight of parafiinic or alkyl aromatic hydrocarbons, in the steam-hydrocarbon mixture, that is dehydrogenated by a single contacting with, or passage over, the employed catalyst under the stated operating conditions Whereas the average total yield represents the proportion by Weight oi' dehydrogenated product `that is producible from a. given quantity of the material to be dehydrogenated by repeatedly returning to contact with the catalyst any undehydrogenated portion of said quantity. The examples follow:

Example No. 1

Minus four to plus 10 mesh granules of a limestone containing about 6% of silica, 1.2% of FezOs, the remainder being essentially CaCOs, were heated at about 650 C. for about three hours in apparatus permitting free evolution of carbon dioxide, thereby providing on said granules a surcial coating consisting essentially of calcium oxide. Over the so-prepared granular catalyst in reactor apparatus a steam-ethylbenzene mixture containing said components in the ratio of 10:1 by volume was continuously flowed at a temperature of about 650 C. for 90 hours. The average per cent conversion of the treated ethylbenzene to styrene was 36% and the average total yield Was 78% by weight, at a contact time of 0.9 second for said mixture. At the end of said 90-hour operating period, the limestone cores of said granular composite catalyst article constituted nearly 60% by Weight of the granular composite catalyst article which Was still highly effective for the purpose when operation was discontinued. The cooled catalyst contained as `a carbon deposit 0.06% by Weight of the treated ethylbenzene, and over 90% of the elemental carbon liberated in the reactor apparatus by pyrolytic reaction, wasl continuously removed as carbon dioxide in the eiuent vapors.

Example No. Z

A sample of marble chips of mesh sizes minus 4 and plus l were heated to 650 C. for three hours while passing thereover steam preheated to said temperature. Thereafter, a steam-ethylbenzene mixture was continuously flowed thereover at a contact time of 0.92 second and at a temperature of 650 C. for 5 days. The average conversion of ethylbenzene to styrene was 35% and the average total yield of styrene was 75% by Weight of treated ethylbenzene. At the end of said 5 days of operation, the marble cores of said composite catalyst article constituted about 55% by Weight thereof. About 0.25% by Weight of the treated ethylbenzene was present as unremoved carbon in the cooled catalyst; about 80% of the formed elemental carbon Was continuously removed from the reactor in the eiiluent vapors.

Example No. 3

Raw granules of Red Flux No. 2, hereinabove referred to and its origin described, and containing about 5% SiOz, 12.5% of FezOs, 47% CaCOs. 31% MgCOa, and a small amount of AlzOs. were introduced into a reactor Vessel Without any preheating or calcining. A vaporous mixture of steam and ethylbenzene in the ratio by volume of 10:1 was preheated to about 650 C. and immediately flowed into contact with the said granules of Red Flux in said reactor. A stream of the said preheated admixture was continuously owed without interruption over the catalyst at a temperature of 650 C. for an operating period of 2.75 days while maintaining a contact time thereof with the catalyst of 0.92 second. During this entire period an average of 48% by Weight of the ethylbenzene brought into contact with the catalyst was continuously converted to styrene and by continuously recycling unconverted ethylbenzene that Was separated from said styrene, an ultimate yield of 74% of styrene was recovered from a given quantity of ethylbenzene.

Example No. 4

A granulated dolomitic limestone containing about 11.5% of S102, 4.6% A1203, 12% FeCOa, 42% CaCOs and 28% MgCOz Was screened and the minus 4 and plus 10 mesh sizes were in admixture precalcined at about 650 C. for three hours under conditions permitting free escape of the evolved gas. In the said limestone, the magnesium and calcium carbonates were in the mole ratio of substantially 111.3. A vaporous stream that Was a mixture of steam and ethylbenzene in the ratio of 10:1 and at a temperature of 650 C. was then continuously owed over the said precalcined dolomitic granules for a period of 2.75 days. The contact time of said mixture with the superficially calcined said limestone was maintained at 0.92 second. During this entire period an average of 41% by weight of the ethylbenzene in said stream was converted to styrene and by recycling of the unconverted ethylbenzene into contact with the catalyst 71% of a given quantity of ethylbenzene was converted to styrene. The catalyst Was still operative to produce styrene at the stated rate when the run was interrupted.

Example No. 5

A vaporous admixture of steam and diethylbenzene in the volume ratio of 10: 1 and at a contact time of 0.8 second Was iiowed at a temperature of 650 C. over dolomitic limestone granules (minus 4 to plus 10 mesh) that had been surcially precalcined at a temperature of about 650 C. for about 3 hours. From 240 parts by Weight of so-treated diethyl'benzene there was obtained 70% by Weight of liquid products which contained 52.2%, 19.7% and 9.9% by Weight respectively of diethylbenzene, styrene, and divinylbenzene. Recycling of the undehydrogenated diethylbenzene into contact with the catalyst gave as a total yield from a given Weight of said compound, 21% of divinylbenzene and 41% of styrene, by Weight.

Example No. 6

Isopropylbenzene in vapor form diluted with 9 volumes of steam was flowed at 0.9 second contact time over dol-omite granules supercially precalcined at 650 C., at a contact time of 0.9 second and at an hourly liquid space velocity of 0.4 and at a temperature of 650 C. From 648 parts by Weight of so-treated isopropylbenzene there 13 were obtained 572 parts by weight of condensed liquid products which contained 32.5%, 13.2%, and 31.0% respectively of isopropylbenzene, styrene, and -methylstyr-ene. Recycling of the un converted isopropylbenzene to the dehydrogenation zone gave a yield of 46% by Weight ofmethyl? styrene from a given quantity of isopropylbenzene.

Emample No. 7

Granular dolomite of minus four to plus ten mesh was calcined for 3 hours at 650 C. Over the so-treated dolomite at a temperature of 650 C. and at a contact time of 1.0 second a mixture of steam and mono-ethylnaphthalene in the molar ratio of 10:1 was continuously flowed for an operating period of 120 hours. During this time the average per cent conversionof the ethyl- Emample No. 8

Granular dolomite was partially calcined by heating the same several hours at 650 C. in lthe presence of an inert gas. A mixture of isobutane and water vapor in molar ratio of 1:5 was then flowed over said calcined granules in reactor apparatus while maintaining their temperature at 650 C., the contact time of said mixture with said granules being 0.4 second. Substantially of the so-treated isobutane was continuously dehydrogenated, about 55% by Weight of the so-converted isobutane being isobutylene and the remainder being propylene. Under substantially the same operating conditions but in the absence of water vapor, substantially 20% of the treated isobutane was also dehydrogenated, about 48% by Weight being isobutylene and the remainder propylene. In the latter case, however, the activity of the novel catalyst was rapidly lost to the deposition of carbon thereon accompanied by -deterioration of its structure.

The present co-inventors, as above set forth, provide important improvements in the art of manufacturing and employing dehydrogenation catalyst compositions. The novel composite catalysts are conveniently and cheaply preparable directly from easily obtainable source materials. They have an improved activity and inherently such rugged structure that they are directly usable in large scale operation without 'special and expensive preparation, such as pilling be variously embodied Within the scope of the claims hereinafter made.

14 We claim: 1. A process for preparing a dehydrogenation catalyst capable of converting to styrene at least 30 percent of the ethylbenzene passed over it at '650 C. in the presence of an excess of steam and at a contact time of approximately one second which comprises heating to a temperature in the range of about 600 to 650 C. a mass of granules of a naturally occurring ferruginous limestone which shows a loss of about 30 to 45 percent by weight upon calcination to a constant Weight, removing from said mass carbon dioxide evolved by the thermal decomposition of said limestone by flowing at least one gas selected from the group consisting of steam and dehydrogenatable hydrocarbons through said mass until a surcial layer of decarbonated material is formed on each granule, and discontinuing removal of carbon dioxide from said mass prior to decarbonation of the major portion of each granule, said major portion constituting the core of said granule.

2. A process for preparing a dehydrogenation catalyst capable of converting to styrene at least 30 percent of the ethylbenzene passed over it at 650 C. in the presence of an excess of steam and at a contact time of approximately one second which comprises heating to a temperature in the range of about 600 to 650 C. a mass of granules of a naturally occuring ferruginous carbonate of calcium and magnesium selected from the group consisting of limestone, dolomite and magnesite and which show a loss of about 30 to 45 percent by Weight upon calcination to a constant weight, and forming solely a surcial layer of decarbonated material on each granule by the vcombination of maintaining the partial pressure of carbon dioxide in said mass below the decomposition pressure of said carbonate by flowing at least one gas selected from the group consisting of steam and dehydrogenatable hydrocarbons through said mass and of discontinuing such treatment of the mass prior to decarbonation of a major portion by weight of each granule, said major portion constituting the core of said granule.

BEN BENNETT CORSON.

GEORGE; ARTHUR WEBB.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,634,505 McCaughey July 5, 1927 1,732,381 Schmidt et al Oct. 22, 1929 1,926,587 Hansgirg Sept. 12, 1933 2,057,402 Tropsch Oct. 13, 1936 2,097,054 Atwood Oct. 26, 1937 2,110,833 Mark et al Mar. 8, 1938 2,122,787 Tropsch July 5, 1938 2,122,790 Tropsch July 5, 1938 2,194,335 Tropsch Mar. 19, 1940 2,217,009 Grosse et al. Oct. 8, 1940 2,343,295 naine Mar. r1, 1944 2,371,809 Drennan Mar. 20, 1945 2,395,875 Kearby Mar. 5, 1946 2,397,218 Sturgeon Mar. 26, 1946 2,444,035 Corson et al. June 29, 1948 FOREIGN PATENTS Number Country Date 819,701 France July 12, 1937 

1. A PROCESS FOR PREPARING A DEHYDROGENATION CATALYST CAPABLE OF CONVERTING TO STYRENE AT LEAST 30 PERCENT OF THE ETHYLBENZENE PASSED OVER IT AT 650* C. IN THE PRESENCE OF AN EXCESS OF STEAM AND AT A CONTACT TIME OF APPROXIMATELY ONE SECOND WHICH COMPRISES HEATING TO A TEMPERATURE IN THE RANGE OF ABOUT 600* TO 650* C. A MASS OF GRANULES OF A NATURALLY OCCURRING FERRUGINOUS LIMESTONE WHICH SHOWS A LOSS OF ABOUT 30 TO 45 PERCENT BY WEIGHT UPON CALCINATION TO A CONSTANT WEIGHT, REMOVING FROM SAID MASS CARBON ATOM DIOXIDE EVOLVED BY THE THERMAL DECOMPOSITION OF SAID LIMESTONE BY FLOWING AT LEAST ONE GAS SELECTED 